From: Andy Soos, ENN
Published June 4, 2013 02:55 PM
Hole in the Sun
Coronal holes are areas where the Sun's corona is darker, and colder,
and has lower-density plasma than average. In this case it looks like a
giant hole in the middle of the sun. These were first found when X-ray
telescopes in the Skylab mission were flown above the Earth's atmosphere
to reveal the structure of the corona. An extensive coronal hole rotated
towards Earth recently (May 28-31, 2013). The massive coronal area is
one of the largest seen in a year or more. Coronal holes are the source
of strong solar wind gusts that carry solar particles out to our
magnetosphere and beyond. Solar wind streams take 2-3 days to travel
from the Sun to Earth, and the coronal holes in which they originate are
more likely to affect Earth after they have rotated more than halfway
around the visible hemisphere of the Sun, which is the case here.
Watching the solar corona is like observing the patterns of clouds
in the sky. They can form all sorts of shapes. In June 2012, for
example, there was a big bird image. Snapped through three of NASA
Solar Dynamics Observatory extreme ultraviolet filters, this current
coronal hole is caused by a low density region of hot plasma.
The Sun's corona, or extended outer layer, is a region of plasma that is
heated to over a million degrees Celsius. As a result of thermal
collisions, the particles within the inner corona have a range and
distribution of speeds described by a Maxwellian distribution. The mean
velocity of these particles is about 145 km/s, which is well below the
solar escape velocity of 618 km/s. However, a few of the particles
achieve energies sufficient to reach the terminal velocity of 400 km/s,
which allows them to feed the solar wind. At the same temperature,
electrons, due to their much smaller mass, reach escape velocity and
build up an electric field that further accelerates ions - charged atoms
- away from the Sun. The corona is one of the sources of the solar
wind.
Solar maximum or solar max is a normal period of greatest solar activity
in the 11 year solar cycle of the Sun. During solar maximum, large
numbers of sunspots appear and the sun's irradiance output grows by
about 0.1%. The increased energy output of solar maxima can impact
global climate and recent studies have shown some correlation with
regional weather patterns.
At solar maximum, the Sun's magnetic field lines are the most distorted
due to the magnetic field on the solar equator rotating at a slightly
faster pace than at the solar poles. The solar cycle takes an average of
about 11 years to go from one solar maximum to the next, with an
observed variation in duration of 9 to 14 years for any given solar
cycle. The cycle is peaking now and is causing increased solar activity
such as coronal holes.
For further information see
Sun Hole.
Corona
image via NASA.
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